Problem: Solve for $r$, $ \dfrac{2r}{4r + 2} = 5$
Explanation: Multiply both sides of the equation by $4r + 2$ $ 2r = 5(4r + 2) $ $2r = 20r + 10$ $0 = 18r + 10$ $-10 = 18r$ $18r = -10$ $r = -\dfrac{10}{18}$ Simplify. $r = -\dfrac{5}{9}$